Owing to the increasing efficiency of modern motor vehicle engines, in particular diesel engines, the dissipated heat that is output by the engine may no longer be sufficient to heat the passenger compartment adequately. For this reason, motor vehicles are provided with electric heating systems that have a heating element for converting the electrical power drawn from an electrical energy source, for example the dynamo or the battery, into heat. A heating system that is made up of two PTC (positive temperature coefficient) heating elements is described, for example, in U.S. Pat. No. 6,002,105. Here, the two heating elements are switched on or off by a regulating system as a function of the heating demands of the passenger compartment.
Furthermore, it is to be noted that in modern motor vehicles the demand for electrical energy is increasing as a result of the increasing use of electronics and electrical loads. This leads, in known heating systems, to a situation in which they can overload the electrical energy source, or are required to be operated in a state below the maximum power as a precaution.
It would therefore be desirable to provide an electric heating system for a motor vehicle and a method for regulating it that ensures that the maximum heating power is made available, while also insuring sufficient availability of the electrical energy source for the loads and for starting the engine.